Introduction

We have recently documented that a sharp lateral boundary exists at the southern edge of the Pacific superplume (To et al., 2005). The set of SHdiff wave forms, which graze the South Pacific superplume, have similar features to those observed previously at the southeastern edge of the African superplume. They both show a rapid shift of the arrival time with respect to azimuth and are followed by postcursors. First, we report the postcursors are explained as refractions from the lateral boundary on the D" region. Second, we report that sharp lateral boundaries also exist not only in the southern edge of the super plume, but also in other regions surrounding the super plume.

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